The present invention relates in general to semiconductor devices, and more particularly to a method and structure for making trench FETs in (110)-oriented silicon on metal (SOM) substrates and having high dielectric constant (high k) gate dielectrics.
Conventional semiconductor manufacturing utilizes a number of processes to form semiconductor structures on substrates. In certain devices, the substrate is used as part of the current conduction path. For example, the substrate plays an important role with the solid state switch which is a key semiconductor structure used for discrete device applications and integrated circuits. Solid state switches include, for example, the power metal-oxide-semiconductor field effect transistor (power MOSFET), the insulated-gate bipolar transistor (IGBT), and various types of thyristors. Some of the defining performance characteristics for the power switch are its on-resistance (i.e., drain-to-source on-resistance, RDSon), breakdown voltage, and switching speed.
Generally, the switching speed, on-resistance, breakdown voltage, and power dissipation of a typical MOSFET device may be influenced by the layout, dimensions, and materials. Industry design practice has sought to keep the on-resistance of the MOSFET as low as possible to lower conducting power loss and increase current densities. For example, in vertical power MOSFET devices, the on-resistance is composed of several resistances such as channel resistance, drift region (epitaxial layer) resistance, and substrate resistance. The on-resistance of such a vertical power MOSFET device (as well as other MOSFET devices) is directly influenced by the type and dimensions of materials used in the drain to source conduction path. Therefore, for a vertical power devices, such as a power MOSFET, the substrate is a critical performance element.
Additionally, the substrate can impact the property and quality of the gate dielectric in the MOSFET. Therefore, the method of forming the gate dielectric plays an important role in determining the performance and reliability of an MOSFET.
Even though conventional techniques have been used for making vertical power devices utilizing various substrate materials, there are limitations associated with these conventional techniques. Some of these limitations are discussed in detail below.
Thus, there is a need for improved techniques for making vertical devices having desirable substrate and dielectric properties while maintaining a simple manufacturing process.